lecture24 - Lecture Outline (Week 13, lecture 2) Wireless...

Lecture Outline (Week 13, lecture 2) Wireless Communications – 2 nd plus Generation (CDMA) Reading: Focus on these notes. Also read 10.3 for more details. 1. Problems with Frequency and Space Resource Allocation for Cellular Systems • 1 st and 2 nd generation systems such as AMPS, TDMA and GSM rely on: • Space division with frequency reuse (SDMA) • Frequency division of allocated spectrum (FDMA) • Time division within a frequency channel (TDMA) • Tradeoff in how these resources are divided. • N , the frequency reuse factor is often large (>10), reducing system capacity. • Placement of base stations often is constrained. Cell shape is irregular. • Density of users is often not uniform. • Need to split cells when the number of users in a cell becomes large. • Allocation of frequency to irregular cells is very complicated. • Handoff of a call from one cell to another is abrupt and complicated 2. Motivation for Code Division Multiple Access (CDMA) • Instead of assignment different frequency channels for cells, all cells use the same and entire frequency band for the system. • Instead of dividing frequency into frequency channels for each phone call, all calls in all cells use the same entire frequency band for the system. • Instead of dividing time into time slots, a phone call transmits continuously when the

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